Computer generated 3-D animations enrich a wide range of human experience, captivating audiences at the movie theaters, gluing garners to their personal computers, and embarking home buyers on virtual tours of new homes. To generate 3-D animations, a 3-D designer creates 3-D computer models of the entities using computer aided design systems (CAD). These models are used to emulate the movement, color, and shape of animated entities, from a dancing baby to space ships trekking through the universe.
3-D models are often composed of graphical components that represent the shapes and surfaces that make up modeled objects. A graphical component is a set of data, procedures, or a combination thereof, used to represent a geometry, such as a curve on the surface of a car. A graphical component may consist of multiple other graphical components, to represent more complex geometry, such as a car or human individual.
3-D models are built by users using a Computer Aid Design (“CAD”) system. The user enters commands and data into the CAD system, and in response, the CAD system generates graphical components. Typically, a user enters commands and data through a graphical user interface (“GUI”).
A GUI is a visual display that allows a user to enter commands and data into a computer system by using user input devices, such as a mouse, to manipulate and interact with user interface controls such as a window, a button, a dialogue box, and graphics that represent graphical components. Typically, a graphical user interface used in a CAD system includes a display in which graphical components are “interactively rendered”. The term interactively rendered refers to responding to user input by updating the display of the graphical components to reflect the user input. Even more, a user may modify graphical components by using an input device to manipulate the rendered graphical components. Thus, the GUI enables users to visualize the graphical components they create and edit.
For example, a user modifies the graphical components depicting a human standing in a room. To change the position of the human within the room, a user uses a mouse to drag the human to a new position within the room. To turn the human around so the human is facing the opposite direction, the user uses the mouse to rotate the human.
GUIs are used to create frames for animations. A frame is the state of a set of graphical components at a particular point in time. Animations are generated by displaying a sequence of frames at a particular frequency, such as thirty times per second. For example, a sequence of frames may be used to animate marbles rolling across the room from the left side of the room to the right. Each frame of the sequence would include a graphical component for each of the marbles. In the first frame, the marbles are at the far left of the room. In the second frame, the marbles are positioned a little closer to the right, and so forth. The marbles are rendered in positions that are shifted in each of the frames, which are displayed in rapid sequence to animate the marbles rolling across the room.
To generate a sequence of frames, a user through the GUI interface on a CAD system, may generate data specifying the state of a subset of the frames referred to as key frames. Subsets of frames are logically interleaved between key frames. The CAD system renders the frames between successive key frames by interpolating the state of graphical components in each of the pair of key frames. For example, a user creates a sequence of key frames by using the GUI to establish the position of each of the marbles in the room, storing data for a key frame, then dragging each of the marbles to their next position, and storing data for another key frame, and repeating these manipulations for each of the remainder of the key frames.
Consequently, to generate a sequence of frames, a user may repetitively perform the same GUI manipulations, as illustrated above. Often, user input that is created by repetitively performing the same kinds of manipulations may be entered more efficiently through the use of a scripting language. A scripting language is computer language that contains instructions that correspond to user input that may be entered through a GUI. This allows users of CAD systems, with little or no training in programming, to develop scripts because the scripting language defines instructions that correspond to ways of entering input through a GUI that are familiar to the user. In addition, the scripting language, like computer languages in general, define control constructs that may be used to control the execution of programs written in a scripting language (“scripts”), including instructions for automatically repeating the execution of a set of instructions, such as a for loop. For example, the following script EX illustrates how lines of instructions may be written in a scripting language to input commands and data more efficiently into a CAD system.                for fr in 1 to 1000 by 10 do(                    delta+=5            create_frame(fr)            move marble1.position(delta,0,0,fr)            move marble2.position(delta,0,0,fr)            move marble3.position(delta,0,0,fr)            move marble4.position(delta,0,0,fr)            move marble5.position(delta,0,0,fr)            store_in_frame(fr)            )                        
The for loop in script EX is repeated 100 times to create key frames used to animate marbles accelerating across the room. During each iteration, the scripting language specifies that:                (1) a new frame should be created that is associated with the time interval represented by integer fr,        (2) five marbles should be moved across the room along the X axis for 100 units at a distance represented by delta, which is increased during each iteration,        (3) the new position of each of the five should be recorded in the key frame by storing data associated with the frame fr.Using text editors, which typically have copy and paste capabilities, creating and running instructions written in a scripting language can be accomplished much more quickly than manually entering corresponding commands through a GUI.        
A limitation of conventional scripting languages is that they do not provide instructions or constructs that correspond to all types of user input that may be entered through a GUI. Because certain types of user inputs are not supported by a scripting language, developers of scripts implement work-arounds, which are often undesirably complex and especially burdensome to program.
One type of user input that is not supported by a scripting language is input that specifies a user input mode. A user input mode may have multiple states, each of which affects how other user input is interpreted by a CAD system. A working coordinate system is an example of a user input mode. The state of the working coordinate system determines what coordinate system is relevant to performing operations that depend on a coordinate system. These states include, for example, WORLD, which corresponds to the world's coordinate system, and LOCAL, which corresponds to the coordinate system that is relative to a particular graphical component upon which an operation is performed (“local coordinate system”). If user input specifies that an object should be rotated about the x-axis, and the working coordinate system is set to WORLD, then the object is rotated around a line that intersects the center of the object and runs parallel to the world's x-axis. If the working coordinate system is LOCAL, then the object is rotated around a line that intersects the center of the object and runs parallel to the object's x-axis, which may not run parallel to the world's x-axis.
In addition, the working coordinate system may be set to a relative state. A relative state specifies a particular graphical component's local working coordinate system. When the working coordinate system is set to a relative state based on a graphical component's local coordinate system, operations specified by user input that depend on a coordinate system are executed based on the particular graphical component's local coordinate system.
Because conventional scripting languages do not support the user input mode working coordinate system, writing scripts that specify operations that are performed relative to a coordinate system can be very complex and tedious. Script developers may have to program formulas to calculate a graphical component's position based on another graphical component's position. Some of the formulas may be extraordinarily complex, even more extraordinarily difficult to program, and involve the application of mathematical principles beyond the training of many script developers.
Developing work-arounds for other user input modes can also be complex and tedious. Based on the foregoing, it is clearly desirable to provide a method which reduces the burden and complexity of developing scripts that provide the functionality provided by user input modes.